IOI2 Appendix VI. features being the blast box D and the reservoir E for the molten metal. The former is now applied to all new cupolas on account of its quiet and steady action, the warmed air passing in at several openings such as M. The reservoir keeps the metal quite hot until required, and there is the usual tapping door G, as well as an air pipe F lined with ganister, and a sight hole H. The charging door c and the damper rods B B are worked from the charging platform L, and the gases escape at A A. The blast pipes j j are governed by valves K K, and there is another sight hole at N. Pp. 6 and 747. Blackening.—Plumbago is now very much used for the facing of moulds, being dusted on like the charcoal powder, and afterwards sleeked with suitable tools. It must be used sparingly owing to its refractory nature, and the consequent tendency to close the sand pores and prevent the escape of gas. Other substances have also been adopted, but plumbago is the best because it lies firmly on the mould during casting, while oak-charcoal dust, though otherwise excellent, has a tendency to float. CHAPTER II. P. 71. Expansion of Cast Iron from the solid to the liquid state. An interesting experiment was made by Sir Thos. Wrightson. He placed a cast-iron ball of 132 oz. weight on a surface of molten cast iron. At first the ball sank below the surface, which shewed it had a greater density than that of the liquid ; but in a few seconds it had just risen level with the surface, having then an equal density with the liquid. Continuing to rise, about 1\- of its volume shewed in ,3 or 4 minutes, and at the end of 6 minutes it had melted away. The top of the ball was connected with a spring balance which carried a pencil that marked the curves shewn in Fig. 925 upon a clock-driven drum. Comparing the pressures on the spring, it appeared that the ball expanded i % before it attained an equal density with the liquid, and a r expansion of 6% caused a total increase of 7% in volume.